1. Field of the Invention
The invention relates to the field of detecting one or several transponders in a predetermined detection region. Within the scope of this technical field the invention relates, in particular, to a process for detecting one or several transponders in a detection region structured into at least two cells, in which a transponder can be detected with reference to a particular cell, as well as a configuration for detecting one or several transponders in a predetermined detection region.
2. Description of the Prior Art
A process for determining the position of a mobile telephone registered as a known telephone within a specific network and referred to as a transponder is used, for example, in the network operation of GSM mobile telephones. The transmitting range of the network providerxe2x80x94the detection regionxe2x80x94is divided into discrete cells. With each cell is associated a transmitting/receiving unit (fixed station) via which the telephone operation is handled in this cell on a frequency specific to this cell. In this respect each cell differs with respect to frequency from the adjacent cells. When a mobile telephone is put into operation in such a cell, it is identified at the network end by transmission of its identity such that with the aid of this identification and knowing the fixed station which has received this identification, it is possible to determine in which cell of the detection region this mobile telephone is located. If the mobile radio subscriber crosses the boundary of such a cell with his transmission- or reception-ready mobile telephone and enters the next adjacent cell, his identification data are received by another fixed station such that it is possible to determine at the network end that this mobile telephone is now within this adjacent cell. However, due to a desired overlapping of the cells, a mobile telephone does not change its frequency at the cell boundary proper but rather only after it is, in fact, already within the adjacent cell. By a time-recursive comparison of the mobile telephone positions it is possible to trace the executed motions retroactively. For carrying out such a process it is therefore necessary that the mobile telephone can operate on all frequencies made available by the network provider. The equipment expenditures required are not inconsiderable.
The communication between a mobile telephone and the fixed station of such a cell takes place on HF bands. Through alternative orientation of the antennas between the mobile telephone and a fixed station associated with a cell, and through shadowing due to environmental factors, reflections as well as differing climatic conditions, the actual course of the cell boundaries often deviates considerably from the theoretical cell boundaries. Factors which cannot be influenced, for example, differing and continuously changing weather conditions, however, lead to the fact that the cell boundaries change continuously. If a mobile telephone is located in the margin area of a first cell, communication can take place in ways that cannot be affected alternatively with the fixed station of the first cell and with the fixed station of the adjacent cell. This gives the impression that the mobile telephone migrates back and forth from one cell into the other, suggesting a situation which, in fact, does not exist. The position detected in this case does not correspond to the actual position.
There are applications in which it is necessary to acquire a highly precise detection of the transition of a transponder from one cell into an adjacent cell.
Building on the above-discussed prior art, the invention is therefore based on the task of proposing a process for detecting one or several transponders in a detection region structured into at least two cells, according to which the transition of the transponder from a first cell into a second cell is improved. The invention is further based on the task of providing a corresponding configuration as well as a preferred use of such configuration.
The task with reference to the detecting process is solved according to the invention by the provision of a process for spatially-resolved detecting a transponder in a detection region structured into at least two adjacent regionally-overlapped cells in which the transponder is detectable with reference to a particular one of the cells. The detecting process comprises the following steps of: (a) providing in each of the at least two adjacent overlapped cells a field with a detectable field characteristic; (b) acquiring the field characteristic of a first of the cells using a sensing unit of the transponder; (c) cyclically transmitting a response signal from a transmitting unit of the transponder containing the acquired field characteristics; (d) receiving the response signal by a receiver which contains response signal information regarding the acquired field characteristic; (e) evaluating the response signal with respect to the information of the acquired field characteristic contained in the receiver; (f) comparing the acquired field characteristic with field characteristics provided in the cells; (g) determining the possible position(s) of the transponder on the basis of the results of the performed comparison; and (h) verifying a position determination, wherein, after the detection of a transponder in the first cell, the field characteristic of the adjacent cell is adjusted such that it differs from that of the first cell.
The task with reference to the configuration is solved according to the invention through the provision of a configuration for detecting a transponder in a detection region structured into at least two adjacent regionally-overlapped cells in which the transponder is detectable with reference to a particular one of the cells. The configuration comprises: (a) a plurality of stationary field-generating devices each associated with a respective one of the cells and for generating a field with detectable field characteristics changing at predetermined time intervals, the devices being operable with identical field characteristics as well as with differing field characteristics; (b) a transponder having a sensing unit operable for acquiring detectable field characteristics or changes thereof and a transmitting unit operable for transmitting response signals in response to the operation of the sensing unit; (c) a receiver for receiving the response signals transmitted by the transmitting unit; and (d) a control and memory device connected to the field-generating devices for driving the field-generating devices and connected to the receiver for evaluating the response signals received by the receiver.
As mentioned above, the detecting process according to the invention uses at least two adjacent cells which regionally overlap and thus form an overlap region. For the sake of simplifying the explanations, in the following description the detecting process on the border of two adjacent cells will be discussed. In each cell a field of magnetic or electromagnetic type is provided. The fields are structured identically and comprise a detectable field characteristic which differ, for example, by different phase positions. In the case of such a field characteristic, only one frequency need be made available. The field characteristic in each cell is thus known. This field characteristic is acquired by the sensing unit associated with the transponder. A transmitting unit also associated with transponder cyclically transmits a response signal having information regarding the acquired field characteristic of the field in a cell. The reception of this response signal indicates that a transponder is located in the field or in the cell having this field characteristic. The field-generating device of the adjacent second cell is now driven such that the field characteristic to be detected of the field in this cell is different from the field characteristic of the field in the first cell.
The two fields of the adjacent cells overlap in the overlap region such that therein a third field characteristic is developed which differs from the field characteristics of the fields of the bordering cells. In contrast to prior known detection processes, here the superimposed field characteristics are utilized as position information. Such a superposition can, for example, also be a cancellation. The superposition regions form a spatially sharp boundary to the bordering fields or cells such that a higher spatial resolution is possible compared to prior known processes for the detection of transponders. If the transponder is moved from the first cell into the overlap region and subsequently into the adjacent second cell, the transponder transmits first the response signals representing the field characteristic of the first cell and, subsequently when it is located in the overlap region, it transmits response signals which are neither assigned to the one nor to the other cell and, upon entering the second cell it transmits such response signals which correspond to the field characteristics of the second cell. The information received in each response signal is verified, for example, by comparison with that of the previously received response signal. If the information received in two successive response signals is identical, the transponder is still located within the same cell or within the same cell region or also in the overlap region. Since the field characteristics of the first cell as well as also of the second cell are known, the transponder is in this case clearly and unambiguously in the second cell if, after transmitting response signals with the information characteristic for the overlap region, it has transmitted repeatedly response signals with the information appropriate for the field characteristic of the second cell. Thus the transition of the transponder from the first cell into the second cell is also detectable. The output of a control signal indicating that the transponder is located in the second cell, usefully takes place only after repeated reception of the response signal typical for the field characteristic of the second cell. The number of the repeated receptions is predetermined.
The detecting process according to the invention, and also correspondingly the configuration according to the invention, can be realized preferably in detection regions of relatively small orders of magnitude wherein a preferred use of such a configuration is intended to detect in spatial resolution a transponder serving as a security tag on merchandise in the exit region of a building in order to determine at which point in time a transponder is, in fact, outside the building. Such information is essential if the transponders are used within a theft protection system as security tags on merchandise to safeguard goods disposed in the building. In such a case the first cell of the detection region is inside the building and the second cell outside the building; the overlap region is disposed so as to cover the door area of the building. Through different field strengths of the two adjacent fields the overlap region can be adapted to the particular circumstances.
An exemplary embodiment provides that the fields in the adjacent cells are formed by low-frequency electromagnetic radiation which in the cells is of the same frequency and synchronous. As a detectable field characteristic the phase position of a field in a cell is used such that with a field adjustment in which adjacent cells contain different fields with respect to their field characteristics, these fields differ with respect to their phase positions. In this case a phase jump between the phase position of the first field and that of the second field is detectable by the transponder.
Especially preferred is an embodiment in which the phase position of fields of adjacent cells are offset by 180xc2x0 with respect to each other. In this case, the overlap region is characterized by a field cancellation, in which region thus no phase position is recognized. A transponder can in this case differentiate between three phase positions: xe2x80x9cphase position 0xc2x0xe2x80x9d, xe2x80x9cphase position 180xc2x0xe2x80x9d, and xe2x80x9cphase position unknownxe2x80x9d. The phase positions, offset by 180xc2x0 with respect to one another, of the two overlapping fields causes the cancellation region to be delineated very sharply from the cell regions proper with respect to a detection of the phase position inherent to these cells. The boundary region between the cell region proper and the overlap region is only a few centimeters. It is therefore possible to determine very precisely, given the appropriately dimensioned overlap region, when a transponder is moved from the overlap region into the cell region proper of a bordering cell. If such a configuration is used within the scope of an above denoted theft protection system, the building boundary can be set up by the corresponding dimensioning of the overlap region such that, after it has been determined with certainty that a transponder is outside of the building, an alarm can already be triggered at a point in time at which the transponder is just directly outside in front of the building door.
When such a configuration is used within the scope of such a theft protection system, it is useful if the spatially-resolved detection process of the transponder is preceded by an anti-collision and identification process. When such an anti-collision and identification algorithm conventionally terminates, therewith the transponder is brought into quiescent mode. If an anti-collision and identification process is succeeded in time by such a spatially-resolved detection process, it is useful not to switch the transponder into sleep mode after the communication is completed but rather to switch it into detection mode.
With the above-described spatially-resolved detection process it can occur that through specific spatial positions of the transponder antenna when moving the transponder through the cells, in particular in the proximity of the overlap region, the field characteristic of an LF transmitter is detected, which field characteristic differs from that of the cell in which the transponder is, in fact, located. In these cases an unknown or false field characteristic is detected by the transponder even though the transponder is, in fact, not in the overlap region. To avoid these cases, each cell is divided into two or more subcells. Each subcell comprises its own field-generating device, for example an LF transmitter. It is further possible to divide a cell within the scope of its subcells by impressing the subcells with fields of differing field characteristics in spatial resolution. When using LF transmitters, the fields of the subcells of one cell are first provided with the same frequency, synchronously and in phase, and that only if a response signal with a first phase position is received by the transponder, the fields of adjacent subcells have different field characteristics, for example different phase positions. The field characteristics of the subcells are subsequently switched back and forth between providing same-phase and different-phase subcells. It would be possible to assign a transponder localized according to protocol repeatedly to the same field characteristic or the same subcell through the response signal transmitted by it. A transponder which assumes alternating positions with each switching-over of the cell operation, which alternating operation toggles in the millisecond range, is initially classified as not being uniquely detectable. However, since such a transponder is moved, it unavoidably is also moved into a cell or subcell region in which it is detectable according to protocol.
When using LF transmitters for providing electromagnetic fields, frequencies between 1 kHz and a few hundred kHz are in particular suitable. For transmitting the response signals of the transponders an HF channel is usefully employed which can be, for example, 433 MHz.
These and other features and advantages of the invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described exemplary embodiments of the invention.